Environmental and application effects on MON 37500 efficacy and phytotoxicity

Experiments were conducted in an environmentally controlled growth chamber to determine the effects of temperature (10/5 or 21/7 C, day/night), soil m oisture (7, 14, or 20%), timing (preemergence [PRE] or postemergence [POST] ), and rate (9 or 18 g ai ha(-1)) of application on MON 37500 efficacy on B romus secalinus L. and toxicity to Triticum aestivum L. MON 37500 reduced B , secalinus plant density an average of 40% but did not reduce T. aestivum density. PRE treatments reduced B. secalinus density 40% compared to 12% wi th POST applications when plants were grown at 10/5 C. Soil moisture level also influenced plant density, with 7.9 planes per pot when soil moisture w as maintained at 7%, compared to 8.5 plants per pot with 14 or 20% soil moi sture. MON 37500 reduced B, secalinus dry weight more at 18 g ha(-1) than a t the 9-g ha(-1) rate when grown at 21/7 C, but no rate response occurred a t 10/5 C. PRE applications of MON 37500 at 10/5 C decreased B. secalinus dr y weight 22% more than PRE applications at 21/7 C or POST applications unde r either temperature regime. However, PRE applications of MON 37500 at 21/7 C decreased T. aestivum biomass an average of 16%, compared to 3% or less with other treatments. At 21/7 C, B. secalinus dry weight decreased 46% as soil moisture increased from 7 to 20%. Bromus secalinus was 10 to 12% less susceptible to MON 37500 when grown at 7% soil moisture at 10/5 C than when grown at the same temperature at 14 or 20% soil moisture. Triticum aestivu m injury was greater at 20% soil moisture under each temperature regime.